Metal colloid-colored glass known as the so-called gold ruby glass has been known since the 17th century. The use of copper (“copper ruby”) is also known for this purpose. The production of silver colloids, for example to make graduations and scales on graduated cylinders and beakers is known. A silver paint composition, i.e. a paste, which comprises a silver salt, a carrier material such as kaolin, ocher, or clay, and a sulfur compound, is applied to the glass surface for this purpose and subsequently the silver ions diffuse into the glass surface in a solid state reaction under reducing conditions and form the colored silver colloid there.
There are differing views regarding metal colloid-colored glass ceramics in the literature. According to GB 863,569 or GB 1,398,315 the metal colloids act as nuclei formers during the ceramicizing of a glass to form a glass ceramic and the metal colloids were not found to color the glass ceramic. A glass that is colored red by a metal colloid, which is converted into a red colored glass ceramic, is described in JP 2003-183047 A. The inventor states that it is difficult to maintain the red color in the desired shade during the conversion of the glass into the glass ceramic. A special glass composition, which contains at least one oxide of a bivalent metal and Bi2O3, is proposed. This sort of colored glass may be converted into a glass ceramic while maintaining its color shade. According to KR 920007014 B a red colored glass ceramic may be manufactured for the construction field from a glass, which is made from a glass batch containing 10 to 20 wt. % of CaO, 0.1 to 2.5 wt. % of S7C12, 1.5 to 2.5 wt. % C and 0.1 to 2.5 wt. % CuO. U.S. Pat. No. 3,839,055 discloses a machinable fluoromica glass ceramic, which contains tetrasilic fluoromica. During manufacture the known standard colored compounds of the transition metal series, the rare earth series, but also colloidal glass coloring agents, such as elemental gold, are added to the glass batch. If the glass is colored immediately prior to founding, a glass containing color streaks, a synthetic marble, is produced by the ceramicizing, which in contrast to natural marble resists breakage and has a clearly improved acid resistance.
The contamination of the glass melt tank by the coloring agents during manufacture of a colored glass ceramic from a colored glass is disadvantageous. Because of this contamination very long maintenance times for removal of the coloring agents result when changing the color shade. Circumstances can be produced in which no colorless glass and/or no colorless glass ceramic can be produced with the same glass melt tank.